This invention relates to a process for the preparation of hydroxyalkylalkylcellulose ethers, more particularly to hydroxyalkylalkylcellulose ethers having C.sub.3 or higher hydroxyalkoxyl functionalities.
Hydroxyalkylalkylcellulose ethers (HAAC) having C.sub.3 or higher hydroxyalkoxyl functionalities are conventionally prepared by reacting alkali cellulose with a C.sub.3 or higher alkylene oxide and an etherifying agent which is not an alkylene oxide such as an alkyl chloride, dialkyl sulfate or halocarboxylic acid. In such conventional processes, the alkylene oxide (AO) and the etherifying agent are charged into a reaction vessel containing this alkali cellulose and the reaction mass allowed to react at elevated temperatures until the desired substitution on the cellulose molecule is obtained.
Unfortunately, however, AO undergoes various reactions under the conditions of conventional cellulose etherification reactions. For example, a molecule of AO can react with a molecule of water and a second AO molecule to form a glycol ether. The AO can also react with the etherifying agent to form ethers therewith. Such side reactions are undesirable because impurities are generated which must be removed from the product, and the overall efficiency of the etherification reaction is drastically reduced. For example, in a typical reaction of alkali cellulose with propylene and methylene chloride under conventional conditions, only about 10 to 25 weight percent of the propylene oxide employed reacts with the alkali cellulose as desired.
It has been attempted to reduce the aforementioned side reactions of AO by carrying out the preparation of HAAC in stages. In such processes, the AO is reacted with the cellulose in the presence of only a small amount of an alkali. Following this reaction, additional alkali is added and the alkylation reaction is run. While such processes have increased efficiency of the AO/alkali cellulose reaction, still higher efficiencies would be desirable.
Accordingly, a process for preparing mixed hydroxyalkylcellulose wherein the efficiency of the AO reaction is increased would be highly desired.